浅埋隧道冻结法施工地表冻胀融沉规律及冻结壁厚度优化研究

浅埋隧道对地表冻胀、融沉变形有严格要求。针对珠机城际轨道交通项目联络通道冻结壁设计改进问题，基于热?力耦合理论，利用有限差分数值计算方法对冻结法施工全过程进行模拟，通过比较研究不同厚度冻结壁模型引起的地表冻胀、融沉变形及隧道管片变形规律，实现冻结壁厚度的优化设计。研究表明：（1）该数值模型可有效模拟地表冻胀、融沉变形，利用已查明数值误差对计算结果进行折减可得到较为准确的实际变形预测值；（2）不同模型地表冻胀、融沉规律大致相同，但变形量及影响范围随冻结壁厚度减小呈递减趋势，当冻结壁厚度为2.5 m及以下时变形基本满足规程要求；（3）土体冻胀、融沉变形并非简单的互逆过程，融沉变形通常大于冻胀变形，平均超出量达40%，应特别注意；（4）冻结壁厚度越大相应产生的冻胀力越大，通过优化冻结壁厚度可有效控制隧道管片附加应力及变形的产生，保护已建隧道结构安全；（5）综合选定2.5 m为冻结壁改进厚度，成果直接应用于4#联络通道冻结法施工，经现场监测表明该优化方案有效、可行，对类似工程冻结壁厚度设计具有较好的推广应用价值。

Research on surface frost heave and thaw settlement law and optimization of frozen wall thickness in shallow tunnel using freezing method

There are strict requirements on surface displacement caused by frost heaving and thawing settlement for the shallow tunnels. To improve the frozen wall design of the contact channel in Zhuhai Urban-Airport Interity Railway transit project, the finite difference numerical calculation method is used to simulate the whole process of the artificial ground freezing method based on the thermal-mechanical coupling theory. The optimal design of the thickness of the frozen wall is achieved by comparing the surface displacement of frost heaving, thaw settlement and the deformation of the tunnel segment in models with different frozen wall thicknesses. Results show that: 1) the finite difference numerical model can effectively predict the development of the surface displacement caused by frost heaving and thaw settlement, and an actual deformation prediction value of high accuracy can be obtained with the known error. 2) The frost heaving and thaw settlement of different models almost have the same feature, but the deformation amount and the influence range decrease with the decrease of the thickness of the frozen wall. When the thickness of the frozen wall is less than 2.5 m, the deformation meets the requirements. 3) The frost heaving and thaw settlement of the soil are not simple reciprocal processes. The thaw settlement is usually larger than the heaving deformation, and the averaged excess amount is around 40%. 4) The greater the thickness of the frozen wall is, the greater the frost heave force is. By optimizing the thickness of the frozen wall, the additional stress and deformation of the tunnel segment can be effectively controlled to protect the structure of the existing tunnel. 5) The thickness of 2.5 m is chosen for the improved frozen wall. The research results are directly applied to the construction of the No. 4 communication channel using the freezing method. Combined with the on-site monitoring test, the deformation of each characteristic point is within a reasonable range, indicating that the optimization scheme is practical and feasible, and can be successfully applied in the design of frozen wall thickness in similar projects.